A virus infection caused by Melolontha melolontha L. (Coleoptera: Scarabacidae) entomopoxvirus (MmEPV) was recorded in 0.87% of 1,260 larvae collected in 2001-2002 in Trabzon, Turkey. The diseased larvae had dark brown or black and white spots, compared to the normal white-cream colour of healthy larvae. MmEPV infections reduced the larval life span from 6 mo to 15 +/- 5 d (Mean +/- S.D.). Based on light and electron microscopic observations, the average length of the spheroids was 5.45 +/- 2.34 mu m (Mean +/- S.D.) and the average width was 2.89 +/- 1.13 mu m (Mean +/- S.D.) (n = 50). The presence of a virus was also demonstrated in a DNA-DNA hybridization assay. The bioassays carried out to determine the infectivity of MmEPV proved its effectiveness against the third-instar larvae of the M. melolontha. The highest insecticidal activity determined in the M. melolontha larvae was 93.3% at the concentration of 7.5x10(6) spheroids/ml. Our results suggest that a Turkish isolate of MmEPV is promising for biological control of the M. melolontha larvae.